Terahertz spectroscopy of N$^{18}$O and isotopic invariant fit of several nitric oxide isotopologs

TL;DR

This study used terahertz spectroscopy to analyze nitric oxide isotopologs, especially N$^{18}$O, and performed an isotopic invariant fit to determine precise spectroscopic parameters for identifying these molecules in space.

Contribution

It provides new high-precision spectroscopic data and an isotopic invariant fit for nitric oxide isotopologs, enhancing their identification in astrophysical observations.

Findings

Determined rotational, fine, and hyperfine structure parameters.

Achieved vibrational, rotational, and Born-Oppenheimer corrections.

Enabled accurate prediction of nitric oxide isotopolog spectra.

Abstract

A tunable far-infrared laser sideband spectrometer was used to investigate a nitric oxide sample enriched in 18O between 0.99 and 4.75 THz. Regular, electric dipole transitions were recorded between 0.99 and 2.52 THz, while magnetic dipole transitions between the 2Pi(1/2) and 2Pi(3/2) spin-ladders were recorded between 3.71 and 4.75 THz. These data were combined with lower frequency data of N(18)$O (unlabeled atoms refer to (14)N and (16)O, respectively), with rotational data of NO, (15)NO, N(17)O, and (15)N(18)O, and with heterodyne infrared data of NO to be subjected to one isotopic invariant fit. Rotational, fine and hyperfine structure parameters were determined along with vibrational, rotational, and Born-Oppenheimer breakdown corrections. The resulting spectroscopic parameters permit prediction of rotational spectra suitable for the identification of various nitric oxide isotopologs especially in the interstellar medium by means of rotational spectroscopy.